(1) Field of the Invention
The present invention relates to a current collector and a method of producing the same, which collector is used for a battery, particularly for a secondary battery such as a lithium secondary battery, lithium-ion battery or polyer battery.
(2) Prior Art
A secondary battery comprises an anode plate, in which an anode Material is applied onto the front and reverse sides of a collector so as to be integrated, and a cathode plate, in which a cathode material is applied onto the front and reverse sides of a collector, a sheet-like separator, which is made of a porous material, for electrically insulating the anode plate and the cathode plate. The anode plate and the cathode plate are put on one another to place the separator therebetween to be a middle layer and these elements are rolled and placed in a receptacle and an electrolyte is absorbed by the separator and thereafter the receptacle is sealed.
Conventionally, the anode plate and the cathode plate (These are called "electrode plate" hereinafter.) are produced by coating a mixed slurry including such as a solvent, and a binder with the both sides of various metal foils for integrating the metal foil with an active material, and then dried or hardened with ultraviolet rays.
In the method of producing the hole plate, it is poor in integrality of the metal foil and the active material, and therefore, as mentioned above, when rolling the electrode plate to place it in a receptacle, it somtimes happens that the metal foil and the active material are separated or peels off each other due to bending deformation of of rolling the same, and as a result, it is difficult to obtain a secondary battery having a desired capacity.
Further, when placing the electrode plate in the receptacle, since the electrode plate is placed in the receptacle in such a state that the electrode plate is deformed with bending force, as mentioned above, the metal foil and the active material of the electrode plate are peeled off gradually due to shock in using the same and as a result it has a problem that a charge-discharge capacity of the secondary battery goes down gradually.
Therefore, a plurality of holes penetrate the metal foil and the active material, which is placed on or laminated with the front and reverse sides of the metal foil, so as to be connected with each other through the penetrated holes, and thereby connection of the active materials of the front and reverse sides and the metal foil may be improved so that it may prevent the active materials from peeling off from the surface of the metal foil.
As mentioned above, to connect the active materials placed or laminated on the front and reverse sides of the metal foil by connecting to each other through the penetrated holes of the metal foil, it is necessary to punch the metal foil to have a plurality of penetrated holes in advance and to coat a side of the penetrated metal foil with a mixed slurry including the active material and another side thereof in the same manner and thereafter the mixed slurry is dried or hardened.
However, since the metal foil is penetrated, the mixed slurry coated with a side of the metal foil, goes into the other side of the metal foil through the penetrated holes and therefore the other side is stained. In this case, when coating the other side of the metal foil with the mixed slurry, it sometimes occurrs lack of uniformity in thickness of the mixed slurry on the other side and as the result it occurrs lack of uniformity of thickness of the active material. Therefore, it has a problem that it is difficult to produce the qualified electrode plate constantly.